Crosslinkable syrup copolymers with aminoalkyl (meth)acryloyl solvent monomers

ABSTRACT

A pre-adhesive syrup polymer composition is described comprising an acid-functional (meth)acrylate copolymer and an aminoalkyl (meth)acryloyl solvent monomer, which when polymerized, provides a pressure-sensitive adhesive and pressure-sensitive adhesive articles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 12/754,121, filed Apr.5, 2010, now allowed, the disclosure of which is incorporated byreference in its entirety herein.

TECHNICAL FIELD OF THE INVENTION

This invention relates to pressure-sensitive adhesives and tape articlesprepared therefrom. The tapes are characterized by exhibiting an overallbalance of adhesive and cohesive characteristics and exceptional loadbearing capabilities at elevated temperatures.

BACKGROUND OF THE INVENTION

Pressure-sensitive tapes are virtually ubiquitous in the home andworkplace. In its simplest configuration, a pressure-sensitive tapecomprises an adhesive and a backing, and the overall construction istacky at the use temperature and adheres to a variety of substratesusing only moderate pressure to form the bond. In this fashion,pressure-sensitive tapes constitute a complete, self-contained bondingsystem.

According to the Pressure-Sensitive Tape Council, pressure-sensitiveadhesives (PSAs) are known to possess properties including thefollowing: (1) aggressive and permanent tack, (2) adherence with no morethan finger pressure, (3) sufficient ability to hold onto an adherend,and (4) sufficient cohesive strength to be removed cleanly from theadherend. Materials that have been found to function well as PSAsinclude polymers designed and formulated to exhibit the requisiteviscoelastic properties resulting in a desired balance of tack, peeladhesion, and shear holding power. PSAs are characterized by beingnormally tacky at room temperature (e.g., 20° C.). PSAs do not embracecompositions merely because they are sticky or adhere to a surface.

These requirements are assessed generally by means of tests which aredesigned to individually measure tack, adhesion (peel strength), andcohesion (shear holding power), as noted in A.V. Pocius in Adhesion andAdhesives Technology: An Introduction, 2^(nd) Ed., Hanser GardnerPublication, Cincinnati, Ohio, 2002. These measurements taken togetherconstitute the balance of properties often used to characterize a PSA.

With broadened use of pressure-sensitive tapes over the years,performance requirements have become more demanding. Shear holdingcapability, for example, which originally was intended for applicationssupporting modest loads at room temperature, has now increasedsubstantially for many applications in terms of operating temperatureand load. So-called high performance pressure-sensitive tapes are thosecapable of supporting loads at elevated temperatures for 10,000 minutes.Increased shear holding capability has generally been accomplished bycrosslinking the PSA, although considerable care must be exercised sothat high levels of tack and adhesion are retained in order to retainthe aforementioned balance of properties.

There are two major crosslinking mechanisms for acrylic adhesives:free-radical copolymerization of multifunctional ethylenicallyunsaturated groups with the other monomers, and covalent or ioniccrosslinking through the functional monomers, such as acrylic acid.Another method is the use of UV crosslinkers, such as copolymerizablebenzophenones or post-added photocrosslinkers, such as multifunctionalbenzophenones and triazines. In the past, a variety of differentmaterials have been used as crosslinking agents, e.g., polyfunctionalacrylates, acetophenones, benzophenones, and triazines. The foregoingcrosslinking agents, however, possess certain drawbacks which includeone or more of the following: high volatility; incompatibility withcertain polymer systems; generation of corrosive or toxic by-products;generation of undesirable color; requirement of a separate photoactivecompound to initiate the crosslinking reaction; and high sensitivity tooxygen.

SUMMARY

Briefly, the present disclosure provides a pre-adhesive, curable syrupcopolymer composition comprising an acid-functional (meth)acrylatesolute copolymer and an aminoalkyl (meth)acryloyl solvent monomer, whichwhen polymerized provides a pressure-sensitive adhesive composition. Thepre-adhesive composition crosslinks by acid-base interactions betweenthe acid groups of the copolymer and the amino groups of the solventmonomer.

The pressure-sensitive adhesives of this disclosure, i.e. thecrosslinked compositions, provide the desired balance of tack, peeladhesion, and shear holding power, and further conform to the Dahlquistcriteria; i.e. the modulus of the adhesive at the applicationtemperature, typically room temperature, is less than 3×10⁶ dynes/cm ata frequency of 1 Hz.

In some embodiments, this disclosure provides an adhesive compositionderived from renewable resources. In particular, the present inventionprovides an adhesive composition derived, in part, from plant materials.In some embodiments, the present invention further provides an adhesivearticle, wherein the substrate or backing is also derived from renewableresources. The increase in the price of oil, and concomitantpetroleum-derived products, has led to volatile prices and supply formany adhesive products. It is desirable to replace all or part of thepetroleum-based feedstocks with those derived from renewable sources,such as plants, as such materials become relatively cheaper, and aretherefore both economically and socially beneficial. Therefore, the needfor such plant-derived materials has become increasingly significant.

In this application “pre-adhesive” refers to the syrup compositioncomprising an acid-functional (meth)acrylate solute copolymer, and anaminoalkyl (meth)acryloyl solvent monomer which may be crosslinked toform a pressure-sensitive adhesive.

“Syrup polymer” refers to a solution of a solute polymer in one or moresolvent monomers, the solution having a viscosity of from 500 to 10,000cPs at 22° C.

In this application, “(meth)acrylic” is inclusive of both methacrylicand acrylic. “(Meth)acryloyl” is inclusive of methacryloyl and acryloyl;i.e. is inclusive of both esters and amides.

As used herein, “alkyl” includes straight-chained, branched, and cyclicalkyl groups and includes both unsubstituted and substituted alkylgroups. Unless otherwise indicated, the alkyl groups typically containfrom 1 to 20 carbon atoms. Examples of “alkyl” as used herein include,but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl,isobutyl, t-butyl, isopropyl, n-octyl, 2-octyl, n-heptyl, ethylhexyl,cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and thelike. Unless otherwise noted, alkyl groups may be mono- or polyvalent.

As used herein, the term “heteroalkyl” includes both straight-chained,branched, and cyclic alkyl groups with one or more heteroatomsindependently selected from S, O, and N with both unsubstituted andsubstituted alkyl groups. Unless otherwise indicated, the heteroalkylgroups typically contain from 1 to 20 carbon atoms. “Heteroalkyl” is asubset of “hydrocarbyl containing one or more S, N, O, P, or Si atoms”described below. Examples of “heteroalkyl” as used herein include, butare not limited to, methoxy, ethoxy, propoxy, 3,6-dioxaheptyl,3-(trimethylsilyl)-propyl, 4-dimethylaminobutyl, and the like. Unlessotherwise noted, heteroalkyl groups may be mono- or polyvalent.

As used herein, “aryl” is an aromatic group containing 6-18 ring atomsand can contain optional fused rings, which may be saturated,unsaturated, or aromatic. Examples of an aryl groups include phenyl,naphthyl, biphenyl, phenanthryl, and anthracyl. Heteroaryl is arylcontaining 1-3 heteroatoms such as nitrogen, oxygen, or sulfur and cancontain fused rings. Some examples of heteroaryl groups are pyridyl,furanyl, pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl, indolyl,benzofuranyl, and benzthiazolyl. Unless otherwise noted, aryl andheteroaryl groups may be mono- or polyvalent.

As used herein, “(hetero)hydrocarbyl” is inclusive of hydrocarbyl alkyland aryl groups, and heterohydrocarbyl heteroalkyl and heteroarylgroups, the later comprising one or more catenary oxygen heteroatomssuch as ether or amino groups. Heterohydrocarbyl may optionally containone or more catenary (in-chain) functional groups including ester,amide, urea, urethane, and carbonate functional groups. Unless otherwiseindicated, the non-polymeric (hetero)hydrocarbyl groups typicallycontain from 1 to 60 carbon atoms. Some examples of suchheterohydrocarbyls as used herein include, but are not limited to,methoxy, ethoxy, propoxy, 4-diphenylaminobutyl,2-(2′-phenoxyethoxy)ethyl, 3,6-dioxaheptyl, 3,6-dioxahexyl-6-phenyl, inaddition to those described for “alkyl”, “heteroalkyl”, “aryl”, and“heteroaryl” supra.

DETAILED DESCRIPTION

The present disclosure provides a pre-adhesive composition comprising anacid-functional (meth)acrylate copolymer and an aminoalkyl(meth)acryloyl solvent monomer, which when polymerized and crosslinked,provides a pressure-sensitive adhesive and pressure-sensitive adhesivearticles.

The (meth)acrylate ester monomer useful in preparing the acid functional(meth)acrylate adhesive copolymer is a monomeric (meth)acrylic ester ofa non-tertiary alcohol, which alcohol contains from 1 to 14 carbon atomsand preferably an average of from 4 to 12 carbon atoms.

Examples of monomers suitable for use as the (meth)acrylate estermonomer include the esters of either acrylic acid or methacrylic acidwith non-tertiary alcohols such as ethanol, 1-propanol, 2-propanol,1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol,2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol, 2-octanol,isooctylalcohol, 2-ethyl-1-hexanol, 1-decanol, 2-propylheptanol,1-dodecanol, 1-tridecanol, 1-tetradecanol, citronellol,dihydrocitronellol, and the like. In some embodiments, the preferred(meth)acrylate ester monomer is the ester of (meth)acrylic acid withbutyl alcohol or isooctyl alcohol, or a combination thereof, althoughcombinations of two or more different (meth)acrylate ester monomer aresuitable. In some embodiments, the preferred (meth)acrylate estermonomer is the ester of (meth)acrylic acid with an alcohol derived froma renewable source, such as 2-octanol, citronellol, dihydrocitronellol.

In some embodiments it is desirable for the (meth)acrylic acid estermonomer to include a high T_(g) monomer, have a T_(g) of at least 25°C., and preferably at least 50° C. Suitable high T_(g) monomers includeExamples of suitable monomers useful in the present invention include,but are not limited to, t-butyl acrylate, methyl methacrylate, ethylmethacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutylmethacrylate, s-butyl methacrylate, t-butyl methacrylate, stearylmethacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobornylacrylate, isobornyl methacrylate, benzyl methacrylate, 3,3,5trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide,and propyl methacrylate or combinations.

The (meth)acrylate ester monomer is present in an amount of 85 to 99.5parts by weight based on 100 parts total monomer content used to preparethe polymer. Preferably (meth)acrylate ester monomer is present in anamount of 90 to 95 parts by weight based on 100 parts total monomercontent. When high T_(g) monomers are included, the copolymer mayinclude up to 30 parts by weight, preferably up to 20 parts by weight ofthe 85 to 99.5 parts by weight of (meth)acrylate ester monomercomponent. In such embodiments, the copolymer may comprise:

-   -   i. 85 to 99.5 parts by weight of an (meth)acrylic acid ester of        non-tertiary alcohol;    -   ii. 0.5 to 15 parts by weight of an acid functional        ethylenically unsaturated monomer;    -   iii. 0 to 10 parts by weight of a non-acid functional,        ethylenically unsaturated polar monomer;    -   iv. 0 to 5 parts vinyl monomer; and    -   v. 0 to 5 parts of a multifunctional (meth)acrylate;    -   based on 100 parts by weight total monomer.

The polymer further comprises an acid functional monomer, where the acidfunctional group may be an acid per se, such as a carboxylic acid, or aportion may be salt thereof, such as an alkali metal carboxylate. Usefulacid functional monomers include, but are not limited to, those selectedfrom ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, ethylenically unsaturated phosphonic acids,and mixtures thereof. Examples of such compounds include those selectedfrom acrylic acid, methacrylic acid, itaconic acid, fumaric acid,crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl(meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, andmixtures thereof.

Due to their availability, acid functional monomers of the acidfunctional copolymer are generally selected from ethylenicallyunsaturated carboxylic acids, i.e. (meth)acrylic acids. When evenstronger acids are desired, acidic monomers include the ethylenicallyunsaturated sulfonic acids and ethylenically unsaturated phosphonicacids. The acid functional monomer is generally used in amounts of 0.5to 15 parts by weight, preferably 1 to 15 parts by weight, mostpreferably 5 to 10 parts by weight, based on 100 parts by weight totalmonomer.

The polar monomers useful in preparing the copolymer are both somewhatoil soluble and water soluble, resulting in a distribution of the polarmonomer between the aqueous and oil phases in an emulsionpolymerization. As used herein the term “polar monomers” are exclusiveof acid functional monomers and aminoalkyl (meth)acryloyl solventmonomers.

Representative examples of suitable polar monomers include but are notlimited to 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone;N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substitutedacrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octylacrylamide; poly(alkoxyalkyl) (meth)acrylates including2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate,2-methoxyethoxyethyl (meth)acrylate, 2-methoxyethyl methacrylate,polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, includingvinyl methyl ether; and mixtures thereof. Preferred polar monomersinclude those selected from the group consisting of 2-hydroxyethyl(meth)acrylate and N-vinylpyrrolidinone. The polar monomer may bepresent in amounts of 0 to 10 parts by weight, preferably 0.5 to 5 partsby weight, based on 100 parts by weight total monomer.

When used, vinyl monomers useful in the (meth)acrylate polymer includevinyl esters (e.g., vinyl acetate and vinyl propionate), styrene,substituted styrene (e.g., α-methyl styrene), vinyl halide, and mixturesthereof. As used herein vinyl monomers are exclusive of acid functionalmonomers, acrylate ester monomers and polar monomers. Such vinylmonomers are generally used at 0 to 5 parts by weight, preferably 1 to 5parts by weight, based on 100 parts by weight total monomer.

In order to increase cohesive strength of the coated adhesivecomposition, a multifunctional (meth)acrylate may be incorporated intothe blend of polymerizable monomers. Multifunctional acrylates areparticularly useful for emulsion or syrup polymerization. Examples ofuseful multifunctional (meth)acrylate include, but are not limited to,di(meth)acrylates, tri(meth)acrylates, and tetra(meth)acrylates, such as1,6-hexanediol di(meth)acrylate, poly(ethylene glycol)di(meth)acrylates, polybutadiene di(meth)acrylate, polyurethanedi(meth)acrylates, and propoxylated glycerin tri(meth)acrylate, andmixtures thereof. The amount and identity of multifunctional(meth)acrylate is tailored depending upon application of the adhesivecomposition. Typically, the multifunctional (meth)acrylate is present inamounts less than 5 parts based on total dry weight of adhesivecomposition. More specifically, the crosslinker may be present inamounts from 0.01 to 5 parts, preferably 0.05 to 1 parts, based on 100parts total monomers of the adhesive composition.

The pre-adhesive syrup polymer composition further comprises anaminoalkyl (meth)acryloyl solvent monomer, in addition to the(meth)acrylate copolymer. The aminoalkyl (meth)acryloyl solvent monomeris present added in amounts of 10 to 90, preferably 50 to 80 parts byweight, relative to 100 parts of the copolymer.

The aminoalkyl (meth)acryloyl solvent monomer is of the general formula:

wherein

R¹ is H or CH₃; X¹ is —O— or —NH—;

R² is an (hetero)hydrocarbyl group, preferably an alkylene group,preferably of 1 to 12 carbon atoms, and which is optionally substitutedwith a hydroxyl group;R³ is H or a C₁-C₁₂ alkyl group,R⁴ is a C₁-C₁₂ alkyl group or (meth)acryloylalkylene, i.e.CH₂═C(R¹)—CO—R⁵—, where R⁵ is a C₂-C₆ alkylene. In embodiments where R⁴is a (meth)acryloylalkylene group, an additional free-radical means ofcrosslinking is provided to the composition.

R² is a straight or branched chain alkylene preferably containing fromone to about six carbon atoms. When R² is alkylene it can also containhetero functional groups such as carbonyl, oxy, or catenary nitrogen,preferably fully substituted catenary nitrogen wherein the substituentis free of hydrogen-donor hydrogen bonding functional groups. In anotherembodiment R² can be arylene (e.g., 1,4-phenylene) or arylenesubstituted by lower alkyl or lower alkoxy R² can also be a combinationof such arylene, alkenylene, and alkylene groups, such as 1,4-xylylene.

The aminoalkyl (meth)acryloyl solvent monomer of Formula I may beprepared as shown in Scheme 1.

wherein

R¹ is H or CH₃; X¹ is —O— or —NH—;

R² is an (hetero)hydrocarbyl group, preferably an alkylene group, whichis optionally substituted with a hydroxyl group;R³ is H or a C₁-C₁₂ alkyl group,R⁴ is a C₁-C₁₂ alkyl group or (meth)acryloylalkylene, andX³ is an alkoxy group or a halide leaving group.

Embodiments in which R² is a hydroxyl substituted alkylene group may beprepared by the addition of a primary or secondary amine to anepoxy-containing (meth)acrylate, such as glycidyl (meth)acrylate asshown in Scheme 2:

As illustrated, the nucleophilic addition of the amine may occur ateither carbon atom of the epoxide group, yielding a mixture of products.Further, it is believed that the free hydroxyl groups may undergotrans-esterification—either intramolecularly or with other acrylatemonomers.

The aminoalkyl (meth)acryloyl solvent monomer may be added to the extantcopolymer. It is believed that the amino group of the aminoalkyl(meth)acryloyl solvent monomer reacts with the pendent acid functionalgroups of the acid functional (meth)acrylate copolymer to form an ioniclinkage, i.e. a quaternary ammonium group. The pendent (meth)acrylategroup may be subsequently free radically polymerized to crosslink thecopolymer. The crosslink in the adhesive composition is an ioniccrosslink (acid-base) between the amino groups and the acid groups.

whereM_(acrylate) represents polymerized (meth)acrylate monomer units derivedfrom (meth)acrylic acid ester of non-tertiary alcohol having “a”polymerized monomer units,M_(acid) represents polymerized monomer units derived from acidfunctional monomers having “b” polymerized monomer units, shown as theconjugate base although the acid may be present;M_(polar) represents polymerized polar monomer units having “c’polymerized monomer units,M_(vinyl) represents polymerized vinyl monomer units derived from acidfunctional monomers having “d” polymerized monomer units, andM_(multi) represents polymerized multifunctional (meth)acrylate monomerunits having “e” polymerized monomer units, andwherein a and b are at least one and c, d, and e may be zero ornon-zero, and

R¹ is H or CH₃; X¹ is —O— or —NH—;

R² is an (hetero)hydrocarbyl group, preferably an alkylene group, whichis optionally substituted with a hydroxyl group;R³ is H or a C₁-C₁₂ alkyl group,R⁴ is a C₁-C₁₂ alkyl group or (meth)acryloylalkylene.

It will be understood that the values of subscripts a to e correspond tothe amounts of the monomers in the polymerizable composition, i.e. 85 to99.5 parts by weight of an (meth)acrylic acid ester monomer; and 0.5 to15 parts by weight of an acid functional monomer. Other monomers may bepresent in the amounts previously recited. In scheme 2, the aminoalkyl(meth)acryloyl crosslinking solvent monomer is shown as the conjugate,but may be present as the base.

A preferred method of preparing acid functional (meth)acrylatecopolymers comprises partially polymerizing monomers to produce a syruppolymer comprising the acid functional (meth)acrylate copolymer andunpolymerized monomers. The syrup polymer composition is polymerized toa useful coating viscosity, which may be coated onto a substrate (suchas a tape backing) and further polymerized. Partial polymerizationprovides a coatable solution of the acid functional (meth)acrylatesolute copolymer in one or more solvent monomers. Generally, theaminoalkyl (meth)acryloyl solvent monomer is added to the partiallypolymerized composition, then coated on a suitable substrate and furtherpolymerized.

For syrup application processing, a preferred monomer mixture (secondcomponent) comprises 85 to 99.5 pbw of one or more (meth)acrylate estermonomers, 0.5 to 15 pbw of acid functional monomers, 0 to 10 pbw of oneor more second, non-acid, polar monomers, and 0 to about 5 pbw of othervinyl monomers, based on 100 parts total monomer. The aminoalkyl(meth)acryloyl solvent monomer may be added to the extant acidfunctional copolymer.

The polymerizations may be conducted in the presence of, or preferablyin the absence of, suitable solvents such as ethyl acetate, toluene andtetrahydrofuran which are unreactive with the functional groups of thecomponents of the syrup polymer.

Polymerization can be accomplished by exposing the syrup polymercomposition to energy in the presence of a photoinitiator. Energyactivated initiators may be unnecessary where, for example, ionizingradiation is used to initiate polymerization. These photoinitiators canbe employed in concentrations ranging from about 0.0001 to about 3.0pbw, preferably from about 0.001 to about 1.0 pbw, and more preferablyfrom about 0.005 to about 0.5 pbw, per 100 pbw of the solventmonomer(s).

A preferred method of preparation of the syrup polymer is photoinitiatedfree radical polymerization. Advantages of the photopolymerizationmethod are that 1) heating the monomer solution is unnecessary and 2)photoinitiation is stopped completely when the activating light sourceis turned off. Polymerization to achieve a coatable viscosity may beconducted such that the conversion of monomers to polymer is up to about30%. Polymerization can be terminated when the desired conversion andviscosity have been achieved by removing the light source and bybubbling air (oxygen) into the solution to quench propagating freeradicals. The solute polymer(s) may be prepared conventionally in anon-monomeric solvent and advanced to high conversion (degree ofpolymerization). When solvent (monomeric or non-monomeric) is used, thesolvent may be removed (for example by vacuum distillation) eitherbefore or after formation of the syrup polymer. While an acceptablemethod, this procedure involving a highly converted functional polymeris not preferred because an additional solvent removal step is required,another material may be required (the non-monomeric solvent), anddissolution of the high molecular weight, highly converted solutepolymer in the monomer mixture may require a significant period of time.

Useful photoinitiators include benzoin ethers such as benzoin methylether and benzoin isopropyl ether; substituted acetophenones such as2,2-dimethoxyacetophenone, available as Irgacure™ 651 photoinitiator(Ciba Specialty Chemicals), 2,2 dimethoxy-2-phenyl-1-phenylethanone,available as Esacure™ KB-1 photoinitiator (Sartomer Co.; West Chester,Pa.), and dimethoxyhydroxyacetophenone; substituted α-ketols such as2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such as2-naphthalene-sulfonyl chloride; and photoactive oximes such as1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularlypreferred among these are the substituted acetophenones.

Preferred photoinitiators are photoactive compounds that undergo aNorrish I cleavage to generate free radicals that can initiate byaddition to the acrylic double bonds. The photoinitiator can be added tothe mixture to be coated after the copolymer has been formed, i.e.,photoinitiator can be added to the syrup polymer mixture. Suchpolymerizable photoinitiators are described, for example, in U.S. Pat.Nos. 5,902,836 and 5,506,279 (Babu et al.).

The syrup polymer composition and the photoinitiator may be irradiatedwith activating UV radiation to polymerize the monomer component(s). UVlight sources can be of two types: 1) relatively low light intensitysources such as Blacklights which provide generally 10 mW/cm² or less(as measured in accordance with procedures approved by the United StatesNational Institute of Standards and Technology as, for example, with aUVIMAP™ UM 365 L-S radiometer manufactured by Electronic Instrumentation& Technology, Inc., in Sterling, Va.) over a wavelength range of 280 to400 nanometers and 2) relatively high light intensity sources such asmedium pressure mercury lamps which provide intensities generallygreater than 10 mW/cm², preferably between 15 and 450 mW/cm². Whereactinic radiation is used to fully or partially polymerize the syruppolymer composition, high intensities and short exposure times arepreferred. For example, an intensity of 600 mW/cm² and an exposure timeof about 1 second may be used successfully. Intensities can range fromabout 0.1 to about 150 mW/cm², preferably from about 0.5 to about 100mW/cm², and more preferably from about 0.5 to about 50 mW/cm². Suchphotoinitiators preferably are present in an amount of from 0.1 to 1.0pbw per 100 pbw of the syrup polymer composition.

Accordingly, relatively thick coatings (e.g., at least about 1 mil or25.4 micrometers) can be achieved when the extinction coefficient of thephotoinitiator is low.

The degree of conversion can be monitored during the irradiation bymeasuring the index of refraction of the polymerizing medium aspreviously described. Useful coating viscosities are achieved withconversions (i.e. the percentage of available monomer polymerized) inthe range of up to 30%, preferably 2-20%, more preferably from 5-15%,and most preferably from 7-12%. The molecular weight (weight average) ofthe solute polymer(s) is at least 100,000, preferably at least 500,000.

When preparing acid functional (meth)acrylate copolymers, it isexpedient for the photoinitiated polymerization reactions to proceed tovirtual completion, i.e., depletion of the monomeric components, attemperatures less than about 70° C. (preferably at 50° C. or less) withreaction times less than 24 hours, preferably less than 12 hours, andmore preferably less than 6 hours. These temperature ranges and reactionrates obviate the need for free radical polymerization inhibitors, whichare often added to acrylic systems to stabilize against undesired,premature polymerization and gelation. Furthermore, the addition ofinhibitors adds extraneous material that will remain with the system andinhibit the desired polymerization of the syrup polymer and formation ofthe crosslinked pressure-sensitive adhesives. Free radicalpolymerization inhibitors are often required at processing temperaturesof 70° C. and higher for reaction periods of more than about 6 to 10hours.

The copolymerizable mixture may optionally further comprise chaintransfer agents to control the molecular weight of the resultantpolymer. Examples of useful chain transfer agents include but are notlimited to those selected from the group consisting of carbontetrabromide, alcohols, mercaptans, and mixtures thereof. When present,the preferred chain transfer agents are isooctylthioglycolate and carbontetrabromide. The emulsion mixture may further comprise up to about 0.5parts by weight of a chain transfer agent, typically about 0.01 to about0.5 parts by weight, if used, preferably about 0.05 parts by weight toabout 0.2 parts by weight, based upon 100 parts by weight of the totalmonomer mixture.

Alternatively, the acid functional copolymers can be prepared by anyconventional free radical polymerization method, including solution,radiation, bulk, dispersion, emulsion, and suspension processes. Theseparately prepared copolymer is then combined with the solvent monomer.The (meth)acrylate polymers may be prepared via suspensionpolymerizations as disclosed in U.S. Pat. Nos. 3,691,140 (Silver);4,166,152 (Baker et al.); 4,636,432 (Shibano et al); 4,656,218(Kinoshita); and 5,045,569 (Delgado). Each describes adhesivecompositions, and the descriptions of polymerization processes areincorporated herein by reference.

Water-soluble and oil-soluble initiators useful in preparing the acidfunctional copolymers are initiators that, on exposure to heat, generatefree-radicals which initiate (co)polymerization of the monomer mixture.Water-soluble initiators are preferred for preparing the (meth)acrylatepolymers by emulsion polymerization. When used, initiators may comprisefrom about 0.05 to about 1 part by weight, preferably about 0.1 to about0.5 part by weight based on 100 parts by weight of monomer components inthe acid functional copolymers.

Polymerization of the acid functional copolymers via emulsion techniquesmay require the presence of an emulsifier (which may also be called anemulsifying agent or a surfactant). Useful emulsifiers for the presentinvention include those selected from the group consisting of anionicsurfactants, cationic surfactants, nonionic surfactants, and mixturesthereof. Preferably, emulsion polymerization is carried out in thepresence of anionic surfactant(s). A useful range of emulsifierconcentration is from about 0.5 to about 8 weight percent, preferablyfrom about 1 to about 5 weight percent, based on the total weight of allmonomers of the emulsion pressure-sensitive adhesive.

In some embodiments, the acid functional (meth)acrylate copolymers maybe prepared by solution methods. A typical solution polymerizationmethod is carried out by adding the monomers, a suitable solvent, and anoptional chain transfer agent to a reaction vessel, adding a freeradical initiator, purging with nitrogen, and maintaining the reactionvessel at an elevated temperature, typically in the range of about 40 to100° C. until the reaction is completed, typically in about 1 to 20hours, depending upon the batch size and temperature. Examples of thesolvent are methanol, tetrahydrofuran, ethanol, isopropanol, acetone,methyl ethyl ketone, methyl acetate, ethyl acetate, toluene, xylene, andan ethylene glycol alkyl ether. Those solvents can be used alone or asmixtures thereof.

It is preferable to coat the pre-adhesive syrup polymer composition soonafter preparation. The pre-adhesive syrup polymer composition,(containing the copolymer, other monomers and aminoalkyl (meth)acryloylsolvent monomer), either as a syrup or solution are easily coated uponsuitable substrates, such as flexible backing materials, by conventionalcoating techniques, then further polymerized, and cured or dried, toproduce adhesive coated sheet materials. The flexible backing materialmay be any material conventionally utilized as a tape backing, opticalfilm or any other flexible material.

The pressure-sensitive adhesives may also contain one or moreconventional additives. Preferred additives include tackifiers,plasticizers, dyes, antioxidants, and UV stabilizers. Such additives canbe used if they do not affect the superior properties of the emulsionpressure-sensitive adhesives.

If tackifiers are used, then up to about 50% by weight, preferably lessthan 30% by weight, and more preferably less than 5% by weight based onthe dry weight of the total adhesive polymer would be suitable. In someembodiments no tackifiers may be used. Suitable tackifiers for use with(meth)acrylate polymer dispersions include rosin acids, rosin esters,terpene phenolic resins, hydrocarbon resins, and cumarone indene resins.The type and amount of tackifier can affect properties such ascontactability, bonding range, bond strength, heat resistance andspecific adhesion.

Adhesive articles may be prepared by coating the adhesive orpre-adhesive composition of a suitable support, such as a flexiblebacking. Examples of materials that can be included in the flexiblebacking include polyolefins such as polyethylene, polypropylene(including isotactic polypropylene), polystyrene, polyester, polyvinylalcohol, poly(ethylene terephthalate), poly(butylene terephthalate),poly(caprolactam), poly(vinylidene fluoride), polylactides, celluloseacetate, and ethyl cellulose and the like. Commercially availablebacking materials useful in the invention include kraft paper (availablefrom Monadnock Paper, Inc.); cellophane (available from Flexel Corp.);spun-bond poly(ethylene) and poly(propylene), such as Tyvek™ and Typar™(available from DuPont, Inc.); and porous films obtained frompoly(ethylene) and poly(propylene), such as Teslin™ (available from PPGIndustries, Inc.), and Cellguard™ (available from Hoechst-Celanese).

Backings may also be prepared of fabric such as woven fabric formed ofthreads of synthetic or natural materials such as cotton, nylon, rayon,glass, ceramic materials, and the like or nonwoven fabric such as airlaid webs of natural or synthetic fibers or blends of these. The backingmay also be formed of metal, metallized polymer films, or ceramic sheetmaterials may take the form of any article conventionally known to beutilized with pressure-sensitive adhesive compositions such as labels,tapes, signs, covers, marking indicia, and the like.

The above-described compositions are coated on a substrate usingconventional coating techniques modified as appropriate to theparticular substrate. For example, these compositions can be applied toa variety of solid substrates by methods such as roller coating, flowcoating, dip coating, spin coating, spray coating knife coating, and diecoating. These various methods of coating allow the compositions to beplaced on the substrate at variable thicknesses thus allowing a widerrange of use of the compositions. Coating thicknesses may vary aspreviously described. The solutions may be of any desirableconcentration, and degree of conversion, for subsequent coating, but istypically between 20 to 70 wt. % polymer solids, and more typicallybetween 30 and 50 wt. % solids, in solvent. The syrup polymers may be ofany desirable concentration for subsequent coating, but is typicallybetween 5 to 20 wt. % polymer solids in solvent monomers—the solventmonomers comprising the aminoalkyl (meth)acryloyl solvent monomer andunreacted monomers of the partially polymerized solute copolymer. Thedesired concentration may be achieved by further dilution of the coatingcomposition, or by partial drying.

The flexible support may also comprise a release-coated substrate. Suchsubstrates are typically employed when an adhesive transfer tape isprovided. Examples of release-coated substrates are well known in theart and include, by way of example, silicone-coated kraft paper and thelike. Tapes of the invention may also incorporate a low adhesionbacksize (LAB) which are known in the art.

EXAMPLES

Objects and advantages of this invention are further illustrated by thefollowing examples. The particular materials and amounts, as well asother conditions and details, recited in these examples should not beused to unduly limit this invention.

Materials

Designation & Abbreviations Name Structure Availability IOA Isooctylacrylate 2OA 2-Octyl acrylate dh-CiA Dihydrocitronellyl acrylate AAAcrylic Acid Irg 651 Irgacure 651 CIBA 2,2-dimethoxy-2- Corporationphenylacetophenone Tarrytown, NY HDDA 1,6-hexanediol diacrylateAminoalkyl (Meth)acryloyl Crosslinking Agents I Di(methylamino)EthylAcrylate DMAEA

Aldrich CAS # [2439-35-2]  II Di(methylamino)Ethyl Methacrylate DMAEMA

Aldrich CAS # [2867-47-2]  III Di(ethylamino)Ethyl Acrylate DEAEA

Aldrich CAS # [2426-54-2]  IV Di(ethylamino)Ethyl Methacrylate DEAEMA

Aldrich CAS # [105-16-8]  V Di(isopropylamino)Ethyl Methacrylate DIAEMA

Scientific Polymer Products, Inc. CAS # [16715-83-6] VIDi(butylamino)Ethyl Methacrylate DBAEMA

See prep VII GMA-DMA

See prep VIII GMA-DEA

See prep IX GMA-DHA

See prep X N—Me—N,N—DEA—DA

See prep

Test Methods Peel Adhesion Test [ASTM D 3330/D 3330M-04]

Two 0.5 inch strips of tape were adhered to a glass plate by rolling a4.5 lb roller onto the tape. The two tape samples were averaged. Forcewas measured in Newtons per decimeter with a platen speed of 90 inchesper minute. Peel adhesion data was then normalized to ounces per inchfor the table below.

Shear Strength Test [ASTM D-3654/D 3654M 06, PSTC-7]

0.5 inch strips of tape were adhered by its adhesive to a stainlesssteel plate and cut down to a 0.5 by 0.5 inch square for roomtemperature or 1.0 inch by 0.5 inch square for 70° C. shears. A weightof 4.5 lbs was rolled over the adhered portion. A 1000 g load wasattached to the room temperature shears and 500 g load for 70° C.shears. Each sample was suspended until failure and/or test terminated.Samples were run in triplicate and averaged for the tables below.

Preparation of Amino Alkyl Acrylates and Diacrylates Preparation ofDi(Butylamino)Ethyl Methacrylate (Compound VI)

A 500 mL round bottomed flask fitted with a magnetic stirrer, heatingmantle, and distillation head was charged with a mixture of methylmethacrylate (100 g, 1.0 mol, available from TCI), 2-dibutylaminoethanol(43.3 g, 0.25 mol, available from Matheson, Coleman and Bell, Norwood,Ohio), aluminum isopropoxide (5.0 g, 24 mmol, available form AlfaAesar), and N-phenyl-1-naphthylamine (2.5 g, 11 mmol, available fromAldrich). The mixture was stirred and heated at 80° C. for one hour. Thetemperature of the reaction mixture was increased 10° C. per hour untila temperature of 110° C. was reached. By this time about 20 mL ofmaterial (methanol and methyl methacrylate) had distilled over from thereaction flask. The reaction mixture was left at room temperatureovernight. The next day, the reaction mixture was heated at 115° C. for2 hours and then heated at 135° C. as material distilled from thereaction flask. After 1 hour at 135° C., the desired product,di(butylamino)ethyl methacrylate, was distilled from the reaction flaskat reduced pressure and collected at a temperature of 113-118° C. at 2.5mm pressure. NMR spectral analyses confirmed the structure of theproduct. The boiling point reported previously for this methacrylate(U.S. Pat. No. 2,138,763 (DuPont)) is 108-109° C. at 2 mm pressure.

Preparation of Amino Alkyl Acrylates: Compounds VIII-IX

In a 4 ounce (118 mL) glass jar were mixed 100 mmol each of glycidylmethacrylate (14.2 g, available from Aldrich) and the appropriate amine.For the dimethylamine reaction, 11.2 g of a 40% solution ofdimethylamine in water were added to the glycidyl methacrylateaccompanied by intermittent cooling of the glass jar in an ice bathuntil the initial exothermic reaction had subsided. For the reactions ofthe other amines, 7.2 g of diethylamine (available from Aldrich) and18.5 g of di-n-hexylamine (available from Pfaltz and Bauer, Stamford,Conn.) were utilized. The dimethylamine reaction mixture was left atroom temperature overnight, while the reaction mixtures of diethylamineand di-n-hexylamine were heated at 80° C. overnight. Distillation of thereaction mixtures at reduced pressure provided the desired products,which in all cases were a mixture of isomers as shown in the abovescheme.

Literature Product Distillation boiling range boiling range VII: GMA-DMA105-110° C. at 1.4 mm  58-62° C. at 0.4-0.5 mm^(a) VIII: GMA-DEA 83-105° C. at 0.25-0.40 mm 105-110° C. at 2 mm^(a) IX: GMA-DHA 153-163°C. at 0.30 mm not reported ^(a)Bodnaryuk, F. N.; Korshunov, M. A.;Mikhlin, V. S.; J. Org. Chem. USSR (English translation) 1972, 8,1368-1373.

Preparation of N-Methyl-N,N-Diethanolamine Diacrylate: Compound X

A 500 mL round bottomed flask fitted with a magnetic stirrer, heatingmantle, and distillation head was charged with a mixture of butylacrylate (231 g, 1.8 mol, available from Aldrich),N-methyldiethanolamine (35.7 g, 0.30 mol, available from Aldrich),titanium (IV) n-butoxide (8.0 g, 24 mmol, available form Alfa Aesar),and N-phenyl-1-naphthylamine (2.5 g, 11 mmol, available from Aldrich).The mixture was stirred and heated at 125° C. for 15 hour. Thetemperature of the reaction mixture was then increased 10° C. per houruntil a temperature of 165° C. was reached. By this time about 200 mL ofmaterial (butanol and butyl acrylate) had distilled over from thereaction flask. The reaction mixture was left at room temperatureovernight. The next day, additional charges of butyl acrylate (100 g,0.78 mol), titanium (IV) n-butoxide (2.0 g, 3 mmol), andN-phenyl-1-naphthylamine (1.0 g, 4 mmol) were added and the reactionmixture was heated at 165° C. for 6 hours as material distilled from thereaction flask. The reaction mixture was then distilled at reducedpressure. Excess butyl acrylate distilled over first, followed by thedesired product, N-methyl-N,N-diethanolamine diacrylate, which wascollected at a temperature range of 140-145° C. at 7 mm pressure. NMRspectral analyses confirmed the structure of the product. The boilingpoint previously reported is 94° C. at 0.4 mm (Korshunov, M. A.;Bodnaryuk, F. N.; J. Org. Chem. USSR (English translation) 1968, 4,1157-1161).

Examples 2-28, 73-75 and Comparative C1 and C72

A one quart jar was charged with 540 g of isooctyl acrylate (IOA, 90parts), 60 g of acrylic acid (AA, 10 parts), and 0.24 g of2,2-dimethoxy-2-phenylacetophenone photoinitiator (Irgacure™ 651, CibaSpecialty Chemicals Inc, 0.04 phr). The monomer mixture was purged withnitrogen for 20 minutes then exposed to low intensity ultravioletradiation until a coatable syrup copolymer was prepared, after which anadditional 0.96 g (0.16 phr) of the photoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the dialkylamine acrylate crosslinking agent as shown in Table 2. Theformulations were then coated on Mitsubishi Hostaphan™ primed polyesterfilm at a 2 mil (˜50 micrometers) thickness for the syrup pre-adhesiveformulations and cured at 560 mJ/cm². The peel and shear data are shownin Table 2.

For comparative purposes, control example using no crosslinking agent(Example C1) was also prepared and tested. Peel adhesion and shearstrength were measured for tapes prepared from these adhesives asdescribed in the test methods above.

TABLE 2 Shear Strength Peel Amount of SS Mode of adhesion ExampleCrosslinker (phr) (minutes) failure (N/dm) IOA/AA 90/10 C1 none — 12cohesive 107.4  2 I 0.2 32 cohesive 85.4  3 I 0.5 537  cohesive 88.8  4I 1 10000+  Not Failed 86.3  5 II 0.2 51 cohesive 102.4  6 II 0.5 633 cohesive 103  7 II 1 10000+  Not Failed 105  8 III 0.2 17 cohesive 108.8 9 III 0.5 16 cohesive 103.2 10 III 1 28 cohesive 105.3 11 IV 0.2 32cohesive 103.8 12 IV 0.5 51 cohesive 109.7 13 IV 1 515  cohesive 109.414 V 0.2 38 cohesive 109.3 15 V 0.5 56 cohesive 107 16 V 1 62 cohesive108.5 17 VI 0.2 15 cohesive 112.7 18 VI 0.5 16 cohesive 115 19 VI 1 25cohesive 114 20 VII 0.2 26 cohesive 112.4 21 VII 0.5 238  cohesive 108.622 VII 1 1933 + 2-bond 100.2 4840 + 11527 23 VIII 0.2 270  cohesive105.4 24 VIII 0.5 10000+  Not Failed 104.1 25 VIII 1 10000+  Not Failed99.9 26 IX 0.2 34 cohesive 111.1 27 IX 0.5 198  cohesive 104 28 IX 110000+  Not Failed 102.4 C72 HDDA 0.5 10000+  Not failed 85.6 73 X 0.2010000+  Not failed 99.4 74 X 0.50 10000+  Not failed 91.5 75 X 1.010000+  Not failed 89.7 MOF = Failure mode legend: (co) stands forcohesive.

Examples 30-47 and Comparative C29

A one quart jar was charged with 480 g of isooctyl acrylate (IOA, 80parts), 114 g of isobornyl acrylate (IBOA, 19 parts), 6 g of acrylicacid (AA, 1 parts), and 0.24 g of 2,2-dimethoxy-2-phenylacetophenonephotoinitiator (Irgacure™ 651, Ciba Specialty Chemicals Inc, 0.04 phr).The monomer mixture was purged with nitrogen for 20 minutes then exposedto low intensity ultraviolet radiation until a coatable syrup copolymerwas prepared, after which an additional 0.96 g (0.16 phr) of thephotoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the dialkylamino acrylate crosslinking agent as shown in Table 3. Theformulations were then coated on Mitsubishi Hostaphan™ primed polyesterfilm at a 2 mil (˜50 micrometers) thickness for the syrup pre-adhesiveformulations and cured at 560 mJ/cm². The peel and shear data are shownin Table 3.

For comparative purposes, control example using no crosslinking agent(Example C29) was also prepared and tested. Peel adhesion and shearstrength were measured for tapes prepared from these adhesives asdescribed in the test methods above.

TABLE 3 IOA/IBOA/AA 80/19/1 Shear Strength Peel Amount on SS Mode ofadhesion Example Crosslinker (phr) (minutes) failure (N/dm) C29 NONE 1cohesive 96.8 30 I 0.1 0 cohesive 96.5 31 I 0.2 1 cohesive 96.0 32 II0.1 0 cohesive 94.8 33 II 0.2 1 cohesive 98.2 34 III 0.1 0 cohesive 98.935 III 0.2 0 cohesive 99.7 36 IV 0.1 1 cohesive 100 37 IV 0.2 0 cohesive98.9 38 V 0.1 1 cohesive 101.3 39 V 0.2 0 cohesive 101.9 40 VI 0.1 0cohesive 97.9 41 VI 0.2 0 cohesive 97.1 42 VII 0.1 0 cohesive 97.0 43VII 0.2 0 cohesive 93.8 44 VIII 0.1 1 cohesive 91.9 45 VIII 0.2 0cohesive 87.1 46 IX 0.1 0 cohesive 96.4 47 IX 0.2 1 cohesive 91.2

Examples 49-66 and Comparative C48

A one quart jar was charged with 570 g of 2-octyl acrylate (2-OA, 95parts), 30 g of acrylic acid (AA, 5 parts), and 0.24 g of2,2-dimethoxy-2-phenylacetophenone photoinitiator (Irgacure™ 651, CibaSpecialty Chemicals Inc, 0.04 phr). The monomer mixture was purged withnitrogen for 20 minutes then exposed to low intensity ultravioletradiation until a coatable syrup copolymer was prepared, after which anadditional 0.96 g (0.16 phr) of the photoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the dialkylamine acrylate crosslinking agent as shown in Table 4. Theformulations were then coated on Mitsubishi, Hostaphan™ primed polyesterfilm at a 2 mil (˜50 micrometers) thickness for the syrup pre-adhesiveformulations and cured at 560 mJ/cm². The peel and shear data are shownin Table 4. For comparative purposes, control example using nocrosslinking agent (Example C3) was also prepared and tested. Peeladhesion and shear strength were measured for tapes prepared from theseadhesives as described in the test methods above.

TABLE 4 2-OA/AA 95:5 Shear Peel Amount Strength on Mode of adhesionExample Crosslinker (phr) SS (minutes) failure (N/dm) C48 None 3cohesive 83.2 49 I 0.2 4 cohesive 83.3 50 I 0.5 9 cohesive 68.3 51 II0.2 2 cohesive 86.7 52 II 0.5 9 cohesive 86.8 53 III 0.2 2 cohesive 85.254 III 0.5 3 cohesive 86.3 55 IV 0.2 3 cohesive 86.9 56 IV 0.5 3cohesive 87.4 57 V 0.2 3 cohesive 87.6 58 V 0.5 3 cohesive 87 59 VI 0.23 cohesive 86.5 60 VI 0.5 3 cohesive 88.9 61 VII 0.2 3 cohesive 85.2 62VII 0.5 8 cohesive 84.8 63 VIII 0.2 25 cohesive 91.4 64 VIII 0.5 242cohesive 87.5 65 IX 0.2 4 cohesive 90.3 66 IX 0.5 11 cohesive 87.3

Examples 68-71 and Comparative C67 and C76

A one quart jar was charged with 540 g of 2-octyl acrylate (2-OA, 90parts), 60 g of acrylic acid (AA, 10 parts), and 0.24 g of2,2-dimethoxy-2-phenylacetophenone photoinitiator (Irgacure™ 651, CibaSpecialty Chemicals Inc, 0.04 phr). The monomer mixture was purged withnitrogen for 20 minutes then exposed to low intensity ultravioletradiation until a coatable syrup copolymer was prepared, after which anadditional 0.96 g (0.16 phr) of the photoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the dialkylamine acrylate crosslinking agent as shown in Table 5. Theformulations were then coated on Mitsubishi, Hostaphan™ primed polyesterfilm at a 2 mil (˜50 micrometers) thickness for the syrup pre-adhesiveformulations and cured at 560 mJ/cm². The peel and shear data are shownin Table 5. For comparative purposes, control example using nocrosslinking agent (Example C67 and C76) was also prepared and tested.Peel adhesion and shear strength were measured for tapes prepared fromthese adhesives as described in the test methods above.

TABLE 5 2-OA/AA 90:10 Shear Peel Amount Strength on Mode of adhesionExample Crosslinker (phr) SS (minutes) failure (N/dm) C67 NONE  624cohesive 92 68 II 1 10000+ Not failed 82 69 IV 1 2069 cohesive 90 70 VII1 10000+ Not failed 82 71 VIII 1 10000+ Not failed 89 C76 HDDA 0.510000+ Not failed 81 78 X 0.20 10000+ Not failed 125 79 X 0.50 10000+Not failed 75 80 X 1.0 10000+ Not failed 103

Examples 81-82

A sixteen-ounce (˜473 mL) jar was charged with 450 g ofdihydrocitronellyl (dh-CiA, 90 parts), 50 g of acrylic acid (AA, 10parts), and 0.2 g of 2,2-dimethoxy-2-phenylacetophenone photoinitiator(Irgacure 651, 0.04 phr). The monomer mixture was purged with nitrogenfor 20 minutes then exposed to low intensity ultraviolet radiation untila coatable syrup copolymer was prepared, after which an additional 0.8 g(0.16 phr) of the photoinitiator was added.

The pre-adhesive polymer syrup was blended with various concentrationsof the DMAEA as shown in examples 81-82 and is based on the weightpercent of pre-adhesive polymer syrup. The formulations were then coatedon Mitsubishi Hostaphan™ primed polyester film at a 2-mil (˜50micrometers) thickness for the syrup pre-adhesive formulations and curedat 500 mJ/cm². Peel adhesion and shear strength were measured for asdescribed in the test methods above. Shear was measured at roomtemperature.

TABLE 6 dh-CiA/AA 90:10 Peel Amount Shear Strength Mode of adhesion ExCrosslinker (phr) on SS (minutes) failure (N/dm) 81 I 0.1 983 cohesive75.5 82 I 0.3 5140 cohesive 68.7

1. A polymer composition comprising the reaction product of: a) a solute copolymer comprising i. 85 to 99.5 parts by weight of an (meth)acrylic acid ester of non-tertiary alcohol; ii. 0.5 to 15 parts by weight of an acid functional monomer; iii. 0 to 10 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer; iv. 0 to 5 parts vinyl monomer, with (b) a solvent monomer of the formula:

wherein R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a (hetero)hydrocarbyl group, R³ is H or a C₁-C₁₂ alkyl group, R⁴ is a C₁-C₁₂ alkyl group or (meth)acryloylalkylene.
 2. The polymer of claim 1 of the formula:

where M_(acrylate) represents polymerized multifunctional (meth)acrylate monomer units derived from (meth)acrylic acid ester of non-tertiary alcohol having “a” polymerized monomer units, M_(acid) represents polymerized monomer units derived from acid functional monomers having “b” polymerized monomer units, M_(poiar) represents polymerized polar monomer units having “c’ polymerized monomer units, M_(vinyl) represents polymerized vinyl monomer units derived from acid functional monomers having “d” polymerized monomer units, and M_(multi), represents polymerized multifunctional (meth)acrylate monomer units having “e” polymerized monomer units, and wherein a and b are at least one and c, d, and e may be zero or non-zero.
 3. The polymer of claim 1 wherein the room temperature modulus is less than 3×10⁶ dynes/cm at a frequency of 1 Hz.
 4. The polymer of claim 1 wherein said copolymer comprises 0.5 to 5 parts by weight of acrylic acid and 1 to 5 parts by weight of a non-acid functional, ethylenically unsaturated monomer.
 5. The polymer of claim 2 wherein the acid functional monomer is selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl (meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, and mixtures thereof.
 6. The polymer of claim 1 comprising 1 to 5 parts of a vinyl monomer selected from vinyl esters, styrene, substituted styrene, vinyl halide, vinyl propionate, and mixtures thereof.
 7. The polymer of claim 1 with the average number of carbon atoms of the non-tertiary alcohol being from about 4 to about
 12. 8. The polymer of claim 1 wherein said non-tertiary alcohol of said (meth)acrylic acid ester of non-tertiary alcohol is selected from 2-octanol or dihydrocitronellol.
 9. The polymer composition of claim 1 comprising 0.5 to 5 parts by weight of non-acid functional, ethylenically unsaturated polar monomers.
 10. The crosslinkable composition of claim 8 wherein said non-acid functional, ethylenically unsaturated polar monomer is selected from 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone; N-vinylcaprolactam; acrylamide; t-butyl acrylamide; dimethylamino ethyl acrylamide; N-octyl acrylamide; poly(alkoxyalkyl) (meth)acrylates; poly(vinyl methyl ether); and mixtures thereof.
 11. The polymer composition of claim 1 comprising 0.5 to 15 parts by weight of acid functional ethylenically unsaturated monomers.
 12. The polymer composition of claim 1 comprising 1 to 5 parts by weight of vinyl monomers.
 13. The polymer composition of claim 1 comprising 0.01 to 5 parts of a multifunctional (meth)acrylate.
 14. A method of preparing a pressure-sensitive adhesive comprising combining; (a) a copolymer comprising i. 85 to 99.5 parts by weight of an (meth)acrylic acid ester of non-tertiary alcohol; ii. 1 to 15 parts by weight of an acid functional monomer; iii. 0 to 10 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer; iv. 0 to 5 parts vinyl monomer, with (b) a solvent monomer of the formula:

wherein R¹ is H or CH₃; X¹ is —O— or —NH—; R² is a (hetero)hydrocarbyl group, R³ is H or a C₁-C₁₂ alkyl group, R⁴ is a C₁-C₁₂ alkyl group or (meth)acryloylalkylene; and (c) polymerizing the mixture.
 15. A compound of the formula:


16. An adhesive (co)polymer comprising polymerized monomers selected from 